As a method for increasing energy efficiency at the time of melting glass raw material in a glass melting furnace, a method is known wherein the glass raw material is granulated into briquettes, and the obtained briquettes are preheated or calcined, and then put into a glass melting furnace (see Patent Document 1). At that time, if the granules are preheated by utilizing the high temperature gas discharged from the glass melting furnace, it is possible to effectively utilize the exhaust heat of the glass melting furnace. Patent Document 1 discloses that in order to pre-heat the briquettes to from 650 to 700° C., it is necessary to bring the temperature of the exhaust gas to at least 800° C., and that if briquettes exceed 800° C. locally at the highest temperature zone in the pre-heating device, the briquettes tend to adhere to one another.
As a method for granulating glass raw material for the production of silicate glass, for example, methods disclosed in Patent Documents 2 and 3 are known. Patent Document 2 discloses a method for tumbling granulation in the presence of water by using a relatively coarse grain silica sand having a particle size in a range of from 20 to 100 mesh, and limestone and dolomite of which 50 equivalent % is at most 100 mesh, and adding sodium hydroxide. According to this method, it is disclosed that limestone and dolomite, and sodium hydroxide, are reacted and cured, whereby granules having a high strength is obtainable. In Patent Document 2, a method for producing granules by compression molding is not disclosed.
In Patent Document 3, a method of producing granules (briquettes) by applying pressure to a mixture of glass raw material and a liquid binder, is disclosed. It is disclosed that sand and an alkali metal carbonate (e.g. soda ash) are used as the glass raw material, and an alkali metal silicate solution is used as the liquid binder. In Patent Document 3, there is no disclosure of the particle size of the glass raw material.